We have examined the activity of different compounds on the frequency of single replication forks stalled at a strong block. Some recent results are summarized here: We have found that inhibitors of poly ADP ribose synthesis, which are used in cancer therapy, increase the frequency of single fork stalling. In contrast, inhibition of the degradation of poly ADP ribose reduces the frequency of single stalled forks. Resveratrol, which has received considerable attention as an anti-aging compound, had no effect on the replication patterns. A compound that enhances the activity of a protein chaperone that improves correct protein folding also reduces the frequency of single fork stalling events. Our results suggest that some small molecule effectors can influence events at the level of the genome, such that the frequency of a genome destabilizing and stress inducing event is reduced. We plan to test additional compounds, and will follow those that show activity in the assay. Our recent demonstration that the assay can be performed in murine hematopoietic stem cells makes it possible to examine the influence of anti aging compounds on the competence of stem cells from aged donors to resist replication stress.